1 / 65

Backup

Backup. http://en.wikipedia.org/wiki/Backup. Backup. Backup refers to making copies of data Copies may be used to restore the original after a data loss Copies are typically called "backups" Backups are useful primarily for two purposes:

aldis
Download Presentation

Backup

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Backup http://en.wikipedia.org/wiki/Backup

  2. Backup • Backup refers to making copies of data • Copies may be used to restore the original after a data loss • Copies are typically called "backups" • Backups are useful primarily for two purposes: • Restore a computer to an operational state following a disaster (disaster recovery) • Restore small numbers of files after they have been accidentally (or deliberately) deleted or corrupted • Backups are typically that last line of defense against data loss • Consequently the least granular and the least convenient to use

  3. Backup • Backup system contains at least one copy of all data worth saving • Data storage requirements are considerable • Organizing this storage space and managing the backup process is a complicated undertaking • Data repository model can be used to provide structure to the storage • There are many different types of data storage devices that are useful for making backups • Many different ways in which these devices can be arranged to provide • geographic redundancy • data security • portability

  4. Backup • Before data is sent to its storage location, it must be selected, extracted, and manipulated • Many different techniques have been developed to optimize the backup procedure • Include optimizations for dealing with • open files • live data sources • compression, encryption, and de-duplication • Many organizations and individuals try to have confidence that the process is working as expected and work to define measurements and validation techniques • It is also important to recognize the limitations and human factors involved in any backup scheme

  5. Backup • Due to overlaps in technology, backups and backup systems are frequently confused with archives and fault-tolerant systems • Backups differ from archives: • archives are the primary copy of data • backups are a secondary copy of data • Backup systems differ from fault-tolerant systems • backup systems assume that a fault will cause a data loss event • fault-tolerant systems assume a fault will not

  6. Storage The base of a backup system

  7. Data repository models

  8. Data repository models • Any backup strategy starts with a concept of a data repository • Backup data needs to be stored somehow • Needs to be organized to a degree • May be as simple as a sheet of paper • List of all backup tapes and the dates they were written • May need to be more sophisticated • Computerized index, catalog, or relational database • Different repository models have different advantages • Closely related to choosing a backup rotation scheme

  9. Backup Schemes

  10. Backup Rotation Schemes • Unstructured • An unstructured repository may simply be a stack of floppy disks or CD-R/DVD-R media with minimal information about what was backed up and when. • Easiest to implement, but probably the least likely to achieve a high level of recoverability

  11. Backup Rotation Schemes • Full + Incrementals • Full + Incremental repository aims to make storing several copies of the source data more feasible • Initially, a full backup (of all files) is taken • Afterwards incrementalbackups can be taken • Only the files that have changed since the previous full or incremental backup • Restoring whole systems to a certain point in time requires: • Locating the full backup taken previous to that time • All the incremental backups taken between that full backup and the particular point in time to which the system is supposed to be restored • Offers a high level of security that something can be restored • Typically used with removable media such as tapes and optical disks • Downside: • Dealing with a long series of incrementals • Large storage media requirements

  12. Backup Rotation Schemes • Full + Differential • Differs slightly from a full + incremental • After the full backup is taken • Each partial backup captures all files created or changed since the full backup • Even though some may have been included in a previous partial backup • Advantages: • Restore involves recovering only the last full backup and then overlaying it with the last differential backup • Less media • Less time to recover • Disadvantages: • Less granular recovery

  13. Backup Rotation Schemes • Mirror + Reverse Incrementals • Similar to a Full + Incrementals repository • Instead of an aging full backup followed by a series of incrementals • Offers a mirror that reflects the system state as of the last backup and a history of reverse incrementals • One benefit of this is it only requires an initial full backup • Each incremental backup is immediately applied to the mirror and the files they replace are moved to a reverse incremental • Model is not suited to use removable media • Every backup must be done in comparison to the mirror

  14. Backup Rotation Schemes • Continuous data protection • Model takes it a Mirror + Reverse a step further • Instead of scheduling periodic backups • System immediately logs every change on the host system • Generally done by saving byte or block-level differences • Rather than file-level differences • Differs from simple disk mirroring • Enables a roll-back of the log • Able to restore an old image of data

  15. Storage media

  16. Storage media • Regardless of the repository model that is used: • Data has to be stored on some data storage medium somewhere

  17. Tape backup Manual Automated Robot

  18. Storage media • Magnetic tape  • Has long been the most commonly used medium for bulk data storage, backup, archiving, and interchange • Tape historically has had an order of magnitude better capacity/price ratio when compared to hard disk • Recently the ratios for tape and hard disk have become a lot closer • Myriad of formats • Many are proprietary or specific to certain markets • e.g. mainframes or a particular brand of personal computer • Tape is a sequential access medium • Access times may be poor • Rate of continuously writing or reading data can actually be very fast • Some new tape drives are even faster than modern hard disks (streaming)

  19. Storage media • Hard disk  • Capacity/price ratio of hard disk has been rapidly improving for many years • Making it more competitive with magnetic tape as a bulk storage medium • Main advantages of hard disk storage are low access times, availability, capacity and ease of use • External disks can be connected via: • Local interfaces like SCSI, USB or FireWire • Longer distance technologies like Ethernet, iSCSI, or Fibre Channel • Some disk-based backup systems support data de-duplication which can dramatically reduce the amount of disk storage capacity consumed by daily and weekly backup data • e.g Virtual Tape Libraries

  20. Storage media • Optical disc • Recordable CD/DVD/Blu-ray can be used as a backup device • Advantages of optical drives is that they can be restored on any machine with a commonly compatible drive • In addition, recordable CD's and DVD’s are relatively cheap • Blu-ray is getting there • Many optical disk formats are WORM type, which makes them useful for archival purposes since the data can't be changed • Other rewritable formats can also be utilized • such as CDRW or DVD-RAM • BluRay Disks dramatically increase the amount of data possible on a single optical storage disk

  21. Storage media • Floppy disk  • During the 1980s and early 1990s, many personal/home computer users associated backup mostly with copying floppy disks • Low data capacity of a floppy disk makes it an unpopular and obsolete choice today • Solid state storage • Also known as flash memory, thumb drives, USB flash drives, CompactFlash, SmartMedia, Memory Stick, Secure Digital cards, etc. • These devices are relatively costly for their low capacity, but offer excellent portability, speed, and ease-of-use

  22. Storage media • Remote backup service  • As broadband internet access becomes more widespread, remote backup services are gaining in popularity • Backing up via the internet to a remote location can protect against some worst-case scenarios such as fire, flood, earthquake or nuclear strike which would destroy any backups in the immediate vicinity along with everything else • Downsides: • Internet connections are typically much slower than the speed of local data storage devices • Can be a problem for people with large amounts of data • Risk associated with putting control of personal or sensitive data in the hands of a third party

  23. Managing the data repository

  24. Managing the data repository • Regardless of the data repository model or data storage media used for backups, a balance needs to be struck between • Accessibility • Security • Cost

  25. Managing the data repository • On-line • On-line backup storage is typically the most accessible type of data storage • Can begin restores in milliseconds • Example: an internal hard disk or a disk array (maybe connected to SAN). • This type of storage is very convenient and speedy • But is relatively expensive • On-line storage is vulnerable to being deleted or overwritten, either by accident, or in the wake of a data-deleting virus payload

  26. Managing the data repository • Near-line • Typically less accessible and less expensive than on-line storage • Still useful for backup data storage • Example: a tape library with restore times ranging from seconds to a few minutes • A mechanical device is usually involved in moving media units from storage into a drive where the data can be read or written

  27. Managing the data repository • Off-line • Similar to near-line, except it requires human interaction to make storage media available • This can be as simple as storing backup tapes in a file cabinet • Typical media access time is more than an hour

  28. Managing the data repository • Off-site vault • To protect against a disaster or other site-specific problem, many people choose to send backup media to an off-site vault • The vault can be: • Simple as the System Administrator’s home office -- or -- • Sophisticated as a disaster hardened, temperature controlled, high security bunker that has facilities for backup media storage

  29. Managing the data repository • Backup site, Disaster Recovery Center (DR Center) • In the event of a major disaster, the data on backup media may not be sufficient to recover • Computer systems onto which the data can be restored and properly configured networks are necessary too • Some organizations have their own data recovery centers that are equipped for this scenario • Other organizations contract this out to a third-party recovery center • Note that because DR site is itself a huge investment, backup is very rarely considered preferred method of moving data to DR site • More typical way would be remote disk mirroring, which keeps the DR data as up-to-date as possible

  30. Selection, extraction and manipulation of data

  31. Selection and extraction of file data • Deciding what to back up at any given time is non-trivial • Backing up too much redundant data, the data repository will fill up too quickly • If don't back up enough data, critical information can get lost

  32. Selection and extraction of file data • Key concept is to only back up files that have changed • Copying files • Copy the files to be backed up to another location using the OS specific copy utility • Filesystem dump  • Copy the filesystem that holds the files in question to another location • Usually involves unmounting the filesystem and running a program like dump • Also known as a raw partition backup. • Can run faster than a backup that simply copies files • Some dump software allows the restore specific files from the dump image • Identification of changes  • Some filesystems have an archive bit for each file that says it was recently changed • Some backup software looks at the date of the file and compares it with the last backup, to determine whether the file was changed • Block Level Incremental  • More sophisticated method of backing up changes to files is to only back up the blocks within the file that changed • Requires a higher level of integration between the filesystem and the backup software • Versioning file system  • Keeps track of all changes to a file and makes those changes accessible to the user • Generally this gives access to any previous version, all the way back to the file's creation time • An example of this is the Wayback versioning filesystem for Linux

  33. Selection and extraction of live data

  34. Selection and extraction of live data • If a computer system is in use while it is being backed up, the possibility of files being open for reading or writing can present a problem • If a file is open, the contents on disk may not correctly represent what the owner of the file intends • This is especially true for database files of all kinds

  35. Selection and extraction of live data • When attempting to understand the logistics of backing up open files • Consider that the backup process could take several minutes to back up a large file • To back up a file that is in use • It is vital that the entire backup represent a single-moment snapshot of the file? • Rather than a simple copy of a read-through • Represents a challenge when backing up a file that is constantly changing • Either the database file • Must be locked to prevent changes • A method must be implemented to ensure that the original snapshot is preserved long enough to be copied, all while changes are being preserved. • Backing up a file while it is being changed, in a manner that causes the first part of the backup to represent data before changes occur to be combined with later parts of the backup after the change results in a corrupted file that is unusable, as most large files contain internal references between their various parts that must remain consistent throughout the file

  36. Selection and extraction of live data • Snapshot backup  • A snapshot is an instantaneous function of some storage systems that presents a copy of the filesystem as if it was frozen in a specific point in time, often by a copy-on-write mechanism • An effective way to back up live data is to temporarily quiesce it (e.g. close all files), take a snapshot, and then resume live operations • At this point the snapshot can be backed up through normal methods. • While a snapshot is very handy for viewing a filesystem as it was at a different point in time, it is hardly an effective backup mechanism by itself. • Open file backup  • Many backup software packages feature the ability to back up open files • Some simply check for openness and try again later • File locking is useful for regulating access to open files • Cold database backup  • During a cold backup, the database is closed or locked and not available to users • Datafiles do not change during the copy so the database is in sync upon restore • Hot database backup  • Some database management systems offer a means to generate a backup image of the database while it is online and usable ("hot") • This usually includes an inconsistent image of the data files plus a log of changes made while the procedure is running • Upon a restore, the changes in the log files are reapplied to bring the database in sync

  37. Selection and extraction of metadata

  38. Selection and extraction of metadata • Not all information stored on the computer is stored in files • Accurately recovering a complete system from scratch requires keeping track of this non-data information also • System description  • System specifications are needed to procure an exact replacement after a disaster • File metadata • Each file's permissions, owner, group, ACLs, and any other metadata need to be backed up for a restore to properly recreate the original environment • Partition layout  • The layout of the original disk, as well as partition tables and filesystem settings, is needed to properly recreate the original system • Boot sector  • Boot sector can sometimes be recreated more easily than saving it • Still, it usually isn't a normal file and the system won't boot without it

  39. Manipulation of data

  40. Manipulation of data • It is frequently useful to manipulate the data being backed up to optimize the backup process • Can improve: • backup speed • restore speed • data security • media usage

  41. Manipulation of data • Compression • Various schemes can be employed to shrink the size of the source data to be stored so that uses less storage space • Compression is frequently a built-in feature of tape drive hardware • Duplication • Sometimes backup jobs are duplicated to a second set of storage media • This can be done to rearrange the backup images to optimize restore speed, to have a second copy at a different location or on a different storage medium

  42. Manipulation of data • De-duplication • When multiple similar systems are backed up to the same destination storage device, there exists the potential for much redundancy within the backed up data • For example, if 20 Windows workstations were backed up to the same data repository, they might share a common set of system files • Data repository only needs to store one copy of those files to be able to restore any one of those workstations • Technique scan be applied at the file level or even on raw blocks of data, potentially resulting in a massive reduction in required storage space • May be done on a server before any data moves to backup media • Sometimes referred to as source/client side de-duplication • Approach also reduces bandwidth required to send backup data to its target media • May be done at the target storage device • Sometimes referred to as inline or back-end de-duplication

  43. Manipulation of data • Encryption • Removable storage media such as backup tapes present a data security risk if they are lost or stolen • Encrypting the data on these media can mitigate this problem, but presents new problems • First: encryption is a CPU intensive process that can slow down backup speeds • Second: once data has been encrypted, it can not be effectively compressed • Redundant data makes cryptanalytic attacks easier • Many encryption routines compress the data as an integral part of the encryption process • Third: security of the encrypted backups is only as effective as the security of the key management policy

  44. Manipulation of data • Staging • Sometimes backup jobs are copied to a staging disk before being copied to tape • Sometimes referred to as D2D2T • Acronym for Disk to Disk to Tape • Useful if there is a problem matching the speed of the final destination device with the source device • Typically true in network-based backup systems • Can also serve as a centralized location for applying other data manipulation techniques

  45. Managing the backup process

  46. Managing the backup process • It is important to understand that backup is a process • As long as new data is being created and changes are being made, backups will need to be updated • Individuals and organizations with anything from one computer to thousands (or even millions) of computer systems all have requirements for protecting data • While the scale is different, the objectives and limitations are essentially the same • Likewise, those who perform backups need to know to what extent they were successful, regardless of scale

  47. Objectives

  48. Objectives • Recovery Point Objective (RPO)  • Point in time that the restarted infrastructure will reflect • Essentially, this is the roll-back that will be experienced as a result of the recovery • The most desirable RPO would be the point just prior to the data loss event • Making a more recent recovery point achievable requires increasing the frequency of synchronization between the source data and the backup repository • Recovery Time Objective (RTO)  • Amount of time elapsed between disaster and restoration of business functions • Data security  • In addition to preserving access to data for its owners, data must be restricted from unauthorized access • Backups must be performed in a manner that does not compromise the original owner's undertaking • Can be achieved with data encryption and proper media handling policies

  49. Limitations • System impacts  • An effective backup scheme will take into consideration the limitations of the situation • All backup schemes have some impact on the system being backed up • If this impact is significant, the backup needs to be time-limited to a convenient backup window or alternate means of protecting data need to be employed • These alternate means tend to be more expensive • Costs of hardware, software, labor  • All types of storage media have a finite capacity with a real cost • Matching the correct amount of storage capacity (over time) with the backup needs is an important part of the design of a backup scheme • Any backup scheme has some labor requirement, but complicated schemes have considerably higher labor requirements • The cost of commercial backup software can also be considerable • Network Bandwidth  • Distributed backup systems can be impacted by limited network bandwidth

  50. Implementation • Meeting the defined objectives in the face of the above limitations can be a difficult task • The tools and concepts below can make that task more achievable • Scheduling  • Using a job scheduler can greatly improve the reliability and consistency of backups by removing part of the human element • Many backup software packages include this functionality • Authentication  • Over the course of regular operations, the user accounts and/or system agents that perform the backups need to be authenticated at some level • The power to copy all data off of or onto a system requires unrestricted access • Using an authentication mechanism is a good way to prevent the backup scheme from being used for unauthorized activity • Chain of trust • Removable storage media are physical items and must only be handled by trusted individuals • Establishing a chain of trusted individuals (and vendors) is critical to defining the security of the data

More Related